The purpose of this 3-year cross-sectional study is to investigate the neurobehavioral effects of HIV-1 infection in black males at risk for AIDS. The primary high-risk categories to be studied are HIV-1 serostatus, drug use, and homosexual/bisexual orientation (H/B) and related risk behaviors. The study seeks to achieve the following five aims: 1. to standardize the neuropsychological (NP) and brain imaging (BI) parameters in seronegative (SN) black non-drug users (D-); 2. to estimate the possible effects of sexual orientation and behavior on NP and BI outcomes in SN black D-; 3. To estimate the possible independent and interaction effects of HIV-1 serostatus, drug use and IQ on NP & BI outcomes in H/B blacks who are asymptomatic (ASP) for AIDS; 4. to estimate the possible effects of AIDS-related symptoms on NP & BI outcomes in H/B seropositive (SSP) black D-; and, 5. to determine whether any of the effects noted above are mediated by psychosocial (PS) factors Two cohorts of black males (18-50 yrs) will be recruited. Cohort 1 (Parent cohort) will comprise a sample of 750 black males that will be classified by HIV-1 serostatus, drug use and sexual orientation into six groups: 100 gay/bisexual ASP/D+, 100 gay/bisexual SN/D+, 100 gay/bisexual ASP/D-, 50 gay/bisexual SSP, 200 gay/bisexual SN/D- (gay comparison), and 200 heterosexual SN/D- (heterosexual comparison). The parent cohort will be tested with a comprehensive battery of NP and PS measures, and basic demographic, history of drug use and sexual practices information will be obtained. The sample of 400 comparison SB will serve as the standardization sample to establish appropriate Np & BI norms (Aim 1), and to test for the effects of sexual orientation and behavior on NP & BI outcomes (Aim 2) The psychosocial hypotheses will be tested on the entire sample. Cohort 2 (Nested cohort) will be a random sample of 250 H/B subjects from the parent cohort and will be tested with comprehensive neuroimaging measures including MRI and SPECT, and used to test for NP, PS and BI differences between the 5 gay/bisexual groups (Aims 3, 4 & 5). It is expected that the results of this study should provide a strong empirical foundation for future research on the neurobehavioral consequences of HIV-1 infection in black men.